public class C {
    public static void main(String[] args) {
        // 此代码演示了变量声明、赋值以及简单的输出操作
                double x = 2.1;
                System.out.println(x + "Hello, world!");
                System.out.println(x);
                int y = 1;
                System.out.println(y);
                int z = 2;
                System.out.println(z);
                int a = 3;
                System.out.println(a);
                int b = 4;
                System.out.println(b);
                int c = 5;
                System.out.println(c);
                switch (a) {
                    case '1':
                        System.out.println("a is 1");
                        
                        break;
                    case '2':
                    case '3':
                        System.out.println("a is 2 or 3");
                        
                        break;
                
                    default:
                        System.out.println("you are supprer boy");
                        break;
                }
    }
}
